The instant invention resides in the art of infrared scanners for determining the temperature of an unknown element by comparison with the temperature of a known or reference element. More particulary, the invention relates to a digital read-out for such scanners.
There are presently known a number of infrared scanners, commonly denoted as "thermo-vision," which fundamentally comprise a closed-channel television utilizing infrared light rather than white light for the desired imagery. The television incorporates an infrared detector, preferably of indium antimonide, which produces on a CRT a view of an object being monitored with "hot" and "cold" spots being denoted by different shades of gray. Gray scales are well known in the art of infrared thermal detectors for producing a thermal picture with hotter regions being progressively whiter and colder regions progressively darker, with all conceivable shades of gray therein between.
Typical of previously known thermal scanners is the model 680 Thermo Vision, as described in "AGA Thermo Vision 680 Operating Manual," published and copyrighted in 1975, and bearing manual number 7010, describing a thermal scanner system manufactured and marketed by AGA INFRARED SYSTEMS AB of Lidingo, Sweden. Such a scanner is of the type described herein and includes a number of options broadening the functional capabilities thereof. For example, the CRT of the infrared scanner may provide an image in color with the various colors of the spectrum relating to the temperature of corresponding areas of the object being viewed. While the color feature reduces the problem inherent in reading a gray scale and determining temperature from various shades of gray, it also has inherent drawbacks in that color ranges associated therewith are evidenced by various shades of color which, again, must be discussed by the eye.
Other features of the thermal scanner to particularly adapt the same for use in sensing temperature anomalies in a tire include the temperature profile adapter which enables the scanning lines composing the normal gray tone thermal picture to be simultaneously displayed on a separate monitor. Yet further, the entire scanning raster may be produced on the CRT to provide a thermal relief map of the temperature variations in the object being scanned, with one signal path in the relief map being produced for each raster line. Finally, with the profile adapter one is capable of running multiple profiles in such a manner as to superimpose all raster lines on top of each other, enabling the user to find the highest temperature point in the entire object by comparing the peak of each raster line with the peak of all other raster lines. It should be appreciated that with the profile adapter, one can run a single raster profile of the subject, a multiple raster profile thereof, or may actually construct a thermal relief of the same.
In known thermal scanners, such as the model 680 Thermo Vision, temperatures are measured by comparing a desired temperature spot in the video image with a known black body temperature reference source in the same field. There is a gray scale at the bottom of the screen which varies in brightness from black on the left to white on the right. There are two videos markers on the screen, one highlighting the reference and the other highlighting the temperature spot to be measured. A calculation is performed based on the distance of the markers from each other and the gain setting of the video amplifier. The result is then correlated to a non-linear curve representative of the response of the indium detector for a given lens opening. Additionally, the reference temperature established by the black body must be in the range of the gray scale in order to get a reading. The operator must also have at his disposal a variable reference with a very large range. Indeed, the prior known systems have required that the black body reference be in the visible range, requiring that such reference be dictated by the adjusted system gain, the black body tracking the sensitivity setting in order that a reading may be obtained. In a very sensitive area, the black body would have to be very close to the target temperature, requiring that the operator sacrifice accuracy for ease of operation.